1. Field of the Invention
This invention generally relates to an electronic musical instrument, and more particularly, to a musical tone information processing system for processing information on musical tones for use in an electronic musical instrument.
2. Description of the Related Art
Hereinafter, a conventional system for processing musical tone information such as envelope data in an electronic musical instrument as shown in FIG. 2 will be described with reference to FIGS. 1 (1) and 4 (1). Referring first to FIG. 4 (1), this figure shows a conventional envelope processing unit in which a current value Y of the voltage of an envelope used in the electronic musical instrument of FIG. 2 is made to approach a target value X in each of an attack time, a decay time and a release time of the envelope, by repeating a process comprised of the steps of multiplying the difference between the target value X and the current value Y by a parameter SP and then adding the result of the multiplication to the current value Y. Referring now to FIG. 1 (1), the target values X in the attack time, the decay time and the release time of the envelope are indicated by the target values I, II and III, respectively.
Referring back to FIG. 4 (1), the current value Y is first inverted by a complementer 51 to a two's complement thereof , and further, the resultant complement is added to the target value X in an adder 52; whereby, the current value Y is subtracted from the target value X and the difference (X-Y) between the values X and Y is evaluated. Subsequently, this difference data (X-Y) is multiplied by the parameter SP in the multiplier 53, and thus "change data" (X-Y).times.SP is obtained. The parameter SP defines the magnitude of the rate of change (hereunder sometimes referred to as the changing rate) of the change data (X-Y).times.SP, and as the value of this parameter SP is increased, the gradient or grade of the envelope curve shown in FIG. 1 (1) in the attack, decay or release time is decreased, and accordingly, the parameter SP has a character similar to a well known character of a time constant. Further, the change data (X-Y).times.SP is added to the current value Y and the result of the addition is obtained as a new current value Y.
Nevertheless, when the current value Y becomes close to the target value X, although the current value Y is not yet equal to the target value X, the difference data (X-Y) or the change data (X-Y).times.SP often becomes equal to 0, due to a truncation error, etc., and thus no matter how often the above-described process for making the current value Y approach the target value X is repeated, the current value Y does not become equal to the target value X but reaches or converges to limit values (hereunder sometimes referred to as actual limit values) I, II, and III, which are slightly different from the corresponding target values, I, II and III as shown in FIG. 1 (1). This hinders the transition from an attack phase (corresponding to the attack time) of the envelope to a decay phase (corresponding to the decay time) thereof, that from the decay phase thereof, to a release phase (corresponding to the release time) thereof, and the complete termination of the release phase thereof.
Therefore, the conventional envelope processing system is provided with a target value regulating device 55, and thus sets a current target value (hereunder sometimes referred to as a regulated target value) XT as a value closer to the current value Y than the original target value X by multiplying the original target value X by value regulating data. Further, along with the regualated target value XT, a new current value Y is supplied to a comparator 56, and when the regulated target value XT is matched with the thus-supplied current value Y, the comparator 56 outputs a coincidence signal to the target value generator 11 and the parameter generator 12 as an achievement signal indicating that the current value Y is matched with the regulated target value XT. Note, for example, where the original target value X is reduced by 10%, the value regulating data is set at 0.9. Furthermore, for example where the current value Y is decreased toward the target value X as in the decay phase of the envelope, and further, the original target value X is increased by 10%, the value regulating data is set at 1.1. Moreover, to regulate the target value X, a constant value may be added to the target value instead of multiplying the original target value by the value regulating data.
Accordingly, the conventional envelope information processing system has drawbacks in that the construction of the circuit is complex, because of the provision of the target value regulating device 55, and that the content of the processing is also complex because of the need to change the value regulating value in accordance with the kind of the target value X. For example, in the above-described case, the original target value X is multiplied by the value regulating data of 0.9 if the value X is the regulated target value I at the terminal point of the attack phase, is multiplied by the value regulating data of 1.1 if the value X is the regulated target value II at the terminal point of the decay phase, and the constant value is added to the original target value X if the value X is the regulated value III at the terminal point of the release time. Namely, in the conventional envelope information processing system, the values of the value regulating data must be changed in turn, and further, the kinds of operations used for obtaining the values of the value regulating data from the multiplication and the addition must be selected. The present invention has been created to eliminate the drawbacks of the conventional system.
Therefore, and object of the present invention is to provide a musical tone information processing system in which a judgement of whether or not the target value is achieved can be easily obtained by using a circuit having a simple structure.